We propose to investigate further: (1) The biological control of isoferritin production by normal and neoplastic cells. (2) Intracellular sites in which molecules of ferritin are assembled from protein subunites and iron. (3) Abnormalities in the proteins of bile secreted by iron-loaded rats. In these investigations, we propose to use (a) rat livers, (b) transplantable rat hepatomas grown in vivo, (c) rat hepatoma cells grown in vitro, and cell clones. The following methods will be applied: cell fractionation by preparative ultracentrifugation, radioimmunoassay, biochemical assays of cell fractions, light microscopy including immunflourescence, analytical ultracentrifugation, electron microscopy. To obtain rat bile the common bile ducts of rats will be cannulated and connected to implanted reservoirs from which the bile will be collected daily. BIBLIOGRAPHIC REFERENCES: Lee, J. C. K., Lee, S. S. C., Schlesinger, K. J., and Richter, G. W. Production of Ferritin by Rat Hepatoma Cells In Vitro. Demonstration of Protein Subunits and Ferritin by Immunoflourescence. Am. J. Pathol. 80: 235-248 (1975). Richter, G. W., Lee, J. C. K., Lee, S. S. C., and Schlesinger K. Immunological Tracing of the Biosynthesis of Ferritin in Cultured Cells. In: Proteins of Iron Storage and Transport in Biochemistry and Medicine (R. R. Crichton, ed.) North-Holland Publishing Company, Amsterdam, 1975, 307-314.